Resistance of rumen bacteria murein to bovine gastric lysozyme
© Domínguez-Bello et al; licensee BioMed Central Ltd. 2004
Received: 25 November 2003
Accepted: 11 May 2004
Published: 11 May 2004
Lysozymes, enzymes mostly associated with defence against bacterial infections, are mureinolytic. Ruminants have evolved a gastric c type lysozyme as a digestive enzyme, and profit from digestion of foregut bacteria, after most dietary components, including protein, have been fermented in the rumen. In this work we characterized the biological activities of bovine gastric secretions against membranes, purified murein and bacteria.
Bovine gastric extract (BGE) was active against both G+ and G- bacteria, but the effect against Gram- bacteria was not due to the lysozyme, since purified BGL had only activity against Gram+ bacteria. We were unable to find small pore forming peptides in the BGE, and found that the inhibition of Gram negative bacteria by BGE was due to an artefact caused by acetate. We report for first time the activity of bovine gastric lysozyme (BG lysozyme) against pure bacterial cultures, and the specific resistance of some rumen Gram positive strains to BGL.
Some Gram+ rumen bacteria showed resistance to abomasum lysozyme. We discuss the implications of this finding in the light of possible practical applications of such a stable antimicrobial peptide.
Lysozymes are beta-N-acetyl-muramyl-hydrolase that disrupt bacterial murein . The most common animal lysozyme is the c type, such as the chicken egg white lysozyme (EWL, 14.3 Kda), found in animal, insects and plants . Monogastric animals possess a single gene for lysozyme c expressed in various tissues  and is thought to be primarily involved in defence against bacterial infections.
In contrast, ruminants have multiple lysozyme genes , and at least four code for a gastric lysozyme that functions as a digestive enzyme. Most dietary components are fermented in the rumen to volatile fatty acids , and the ruminant benefits of digesting foregut bacteria as a source of amino acids. Cow gastric lysozyme is a basic enzyme adapted to act in the harsh gastric conditions, with optimal activity at low pH (4.5–5.2), low ionic strength values, and resistant to acid and pepsin [6, 7]. We have previously reported that the recruitment of lysozyme as a gastric digestive enzyme has convergently occurred in the avian foregut fermenter hoatzin , also with multiple gene duplication events during its evolution . Amino acid differences between homologous proteins from different species may have adaptive significance, as is the case with gastric lysozymes. Lysozymes from the stomachs of cows and langur monkeys (both with fermentation in the foregut) are subject to positive darwinian selection [10, 11].
Rumen bacteria represent an important component of the rumen biomass  and is a likely factor exerting evolutionary pressure on gastric lysozyme and other gastric secretions in herbivores with foregut fermentation. This prompted us establish 2 hypotheses: 1 – there might be other abomasum peptides with antimicrobial activity in addition to lysozyme, that would also act against Gram negative bacteria; 2 – since rumen bacteria have been subject to the selective pressure of gastric antimicrobial secretions, rumen bacteria might have developed resistance to these compounds. The objective of this work was to characterize the biological activities of bovine gastric secretions against membranes, purified murein and bacteria.
Cow abomasum mucosa yielded 26.4 mg BGE per g of tissue (1.32 g, of lyophilized extract per 100 ml of acetic extract from 50 g wet mucosa, sd 0.61, N = 20). Protein content of extracts was 60%, equivalent to 16 mg protein per gram of gastric tissue. A total of 5 g of gastric extract was subject to chromatography, and 82,2 mg of active (lytic) protein were obtained. This represents a yield of 1.64% w/w of lysozyme from the crude extract, and 0.43 mg of lysozyme per gram of tissue.
Percentage of growth of control cultures at 6 hours, of Gram+ and Gram- bacteria grown in the presence of EW lysozyme, BG lysozyme and BGE.
Egg White Lysozyme150 ug/ml
Bovine Gastric Lysozyme150 ug/ml
Bovine Gastric Extract10 mg/ml
Muramidase activity in the acid stomach of a foregut fermenter, receiving a considerable biomass of bacteria, allows the digestion of bacterial cell walls and liberalisation of amino acid-rich cell contents. The activity of BG lysozyme on purified murein was different to that of other c lysozymes in having lower optimal pH and L, D carboxypeptidase or Nacetyl muramyl L-ala amidase activity. It was, like other lysozymes, active only against Gram positive bacteria. Other systems such as Entamoeba histolytica, are known to contain lysozyme acting in concert with membrane permeabilizing peptides , but attempts to purify active small peptides from BGE have failed, so far.
Presence of Gram negative bacteria in the rumen does not seem to have driven the evolution of gastric peptides capable of degrade them. This would limit the efficiency of the system, since only Gram positive bacteria are amenable to digestion, and Gram negative bacteria represent a considerable proportion of rumen bacterial biomass. Furthermore, some rumen Gram positive bacteria seem to have developed resistance to the action of BG lysozyme. Rumen bacterium Streptococcus bovis can develop resistance to the pore-forming peptide nisin, by modifying cell lipoteichoic acids. Acquisition of nisin resistance also conferred lysozyme resistance . Little is known about bacteria developing resistance to lysozymes from the host they colonize, as in the case of rumen bacteria and gastric bovine lysozyme. The phenomenon might reflect the selective pressure of the gastric enzyme on rumen bacteria, since BGL-resistant bacteria will be more likely to colonize the lower gut and the rumen of young animals, than BGL-sensitive strains.
The search for new antibacterial drugs has lead to explore more speculative approaches to destroy or inhibit pathogen microorganisms and viruses. It is tempting to optimistically predict that highly stable peptides that naturally evolved as gastric antimicrobials may have a high potential for clinical applications. Human lysozyme (secreted by monocytes), while playing a protective role against infections, depresses superoxide generation of neutrophyls and enhances lymphocyte proliferative response [14–17]. EWL has been applied against bacterial and viral infections, based on its immune-stimulation and anti-inflammatory properties .
Ruminant BG lysozymes, having evolved in a very hostile environment such as the stomach, have developed resistance to acid and proteolysis, and may hold promising uses in treating infections, and in the food industry. In the animal production industry, the uses of antibiotics and hormones as growth promoters has posed health threats to humans and animals, and feed supplementation with some growth promoters is now illegal. The use of new growth promoters that don't pose problems of resistance is a priority, and antimicrobial peptides are of course good candidates. Indeed, lysozyme has been found to be as effective as conventional antibiotics, in promoting growth of poultry . However, the discovery of the capacity of bacteria to presumably modify its bacterial murein and become resistant to the lytic action of lysozymes, will surely be of concern in practical applications, as has bacterial antibiotic resistance.
This work shows that gastric bovine lysozyme is active against Gram positive bacteria but that some rumen strains are unaffected by the enzyme. Possible practical applications of this antimicrobial peptide as an alternative to antibiotics may be limited by the development of bacterial resistance to the lytic action of lysozymes.
Gastric extract and lysozyme purification
Acetic acid extract from abomasal mucosa was prepared as described by Dobson et al. . Bovine gastric extracts (BGE) were lyophilised and kept frozen. BGE proteins were separated by denaturing and non-denaturing PAGE electrophoresis. Band lytic activity was revealed on an overlaying agarose gel embedded with M. luteus. Purification of BG lysozyme was performed re-dissolving lyophilised BGE in 10 vol. of 10% acetic acid, centrifuging at 150,000 × g at 4°C for 1 h. The resulting supernatant, was diluted 1:2.5 with 20% acetonitrile/0.08% trifluoroacetic acid. The material was passed in 0.5 ml batches over a Superdex Pep 10/30 column (Pharmacia LKB) equilibrated with 20% acetonitrile/0.08% trifluoroacetic acid at 20°C and a flow rate of 0.1 ml/min. Active fractions were pooled, diluted 1:2 with starting buffer (50 mM sodium-acetate, pH 4.5) and loaded onto a Mono S 5/5 cation-exchange column (Pharmacia LKB) equilibrated with starting buffer. Adsorbed protein was eluted by washing the column with the same buffer (5 ml) and by use of a 0–500 mM NaCl gradient (15 ml) and a final wash of 1 M NaCl at 10°C. Active material was diluted 1:13 with starting buffer (50 mM sodium-acetate, pH 7.8) and applied again to a Mono S HR 5/5 column (Pharmacia LKB) equilibrated with starting buffer. The column was washed with the same buffer (5 ml) and developed with a 15-ml gradient of 0–500 mM NaCl at 10°C. Active fractions were pooled and stored at -20°C. Reversed-phase HPLC was performed on an Aquapore Butyl 300 column (2.1 × 30 mm; Brownlee Labs) connected with a 130 A separation system (Applied Biosystems). Elution was done with a linear gradient of 0–84% acetonitrile in 0.1% trifluoroacetic acid at 30°C over 45 min. A flow rate of 0.2 ml min-1 was applied, the effluent was monitored by absorbance at 214 nm. Peak fractions were collected manually and tested immediately for lysozyme activity using the lysoplate technique . Tricine-SDS electrophoresis was performed in 13% separation gels .
Lytic activity against M. luteus was determined by scattering changes in a suspension of Micrococcus luteus (0.25 mg/ml in acetate buffer) . Egg white (EW) lysozyme (Sigma) was used as a control. Specific activity per ug of gastric extract was defined as units of activity of 1 ng of EWL on M. luteus, at pH 5.5. Inhibitory effect on bacterial growth was determined on broth and agar lysoplates . Microdilution susceptibility test  was used to determine minimal inhibitory concentrations. Effect of BGE or BG lysozyme on bacterial growth was determined in broth cultures in which growth was monitored turbidimetrically (A600 nm).
Muramidase activity of BGE was assayed on purified E. coli murein  with cellosyl (Hoechst, Frankfurt am Main; 50 μg/ml) and gastric extract (500 μg/ml), determining by HPLC the production of soluble low molecular weight muropeptides . A control without murein was included in the runs and gave no peaks. When required, produced muropeptides were collected individually at the UV detection outlet, vacuum dried, resuspended in MilliQ water and desalted as previously described .
Membrane-permeabilyzing activity of gastric extracts was determined fluorimetricaly, by the liberation of carboxyfluorescein (CF) from brush border membrane vesicles from pig intestinal brush border  and by dissipation of a valinomycin-induced diffusion potential in liposomes .
- Fleming A: On a remarkable bacteriolytic element found in tissues and secretions. Proc Roy Soc London. 1922, B39: 306-317.View ArticleGoogle Scholar
- Prager EM, Jolles P: Animal lysozymes c and g: an overview. Lysozymes: model enzymes in Biochemistry and Biology. Edited by: P Jolles. 1996, Basel/Boston/Berlin, Birkhauser, 9-31.View ArticleGoogle Scholar
- Yu M, Irwin DM: Evolution of stomach lysozyme: the pig lysozyme gene. Mol Phylogenet Evol. 1996, 5: 298-308. 10.1006/mpev.1996.0025.View ArticlePubMedGoogle Scholar
- Irwin DM, Wilson AC: Multiple cDNA sequences and the evolution of bovine stomach lysozyme. J Biol Chem. 1989, 264: 11387-11393.PubMedGoogle Scholar
- Van Soest PJ: Nutrition Ecology of the Ruminant. 1982, Ithaca, New York, Cornell University PressGoogle Scholar
- Pahud JJ, Widmer F: Calf rennet lysozyme. Biochem J. 1982, 201: 661-664.PubMed CentralView ArticlePubMedGoogle Scholar
- Dobson DE, Prager EM, Wilson AC: Stomach lysozymes of ruminants. I. Distribution and catalytic properties. J Biol Chem. 1984, 259: 11607-11616.PubMedGoogle Scholar
- Ruiz MC, Dominguez-Bello MG, Michelangeli F: Gastric lysozyme in the hoatzin (Opisthocomus hoazin), an avian folivore. Experientia. 1994, 50:: 499-501.View ArticleGoogle Scholar
- Kornegay JR: Molecular genetics and evolution of stomach and nonstomach lysozymes in the hoatzin. J Mol Evol. 1996, 42: 676-684.View ArticlePubMedGoogle Scholar
- Messier W, Stewart CB: Episodic adaptive evolution of primate lysozymes. Nature. 1997, 385: 151-154. 10.1038/385151a0.View ArticlePubMedGoogle Scholar
- Yang Z: Likelihood ratio tests for detecting positive selection and application to primate lysozyme evolution. Mol Biol Evol. 1998, 15: 568-573.View ArticlePubMedGoogle Scholar
- Jacobs T, Leippe M: Purification and molecular cloning of a major antibacterial protein of the protozoan parasite Entamoeba histolytica with lysozyme-like properties. Eur J Biochem. 1995, 231: 831-838.View ArticlePubMedGoogle Scholar
- Mantovani HC, Russell JB: Nisin resistance of Streptococcus bovis. Appl Environ Microbiol. 2001, 67: 808-813. 10.1128/AEM.67.2.808-813.2001.PubMed CentralView ArticlePubMedGoogle Scholar
- Das S, Banerjee S, Gupta JD: Experimental evaluation of preventive and therapeutic potentials of lysozyme. Chemotherapy. 1992, 38: 350-357.View ArticlePubMedGoogle Scholar
- Gordon LI, Douglas SD, Kay NE, Yamada O, Osserman EF, Jacob HS: Modulation of neutrophil function by lysozyme. Potential negative feedback system of inflammation. J Clin Invest. 1979, 64: 226-232.PubMed CentralView ArticlePubMedGoogle Scholar
- Osserman EF, Klockars M, Halper J, Fischel RE: Effects of lysozyme on normal and transformed mammalian cells. Nature. 1973, 243: 331-335.View ArticlePubMedGoogle Scholar
- Rinehart JJ, Cerilli JG, Jacob HS, Osserman EF: Lysozyme stimulates lymphocyte proliferation in monocyte-depleted mixed lymphocyte cultures. J Lab Clin Med. 1982, 99: 370-381.PubMedGoogle Scholar
- Sava G: Pharmacological aspects and therapeutic applications of lysozymes. Exs. 1996, 75: 433-449.PubMedGoogle Scholar
- Humphrey BD, Huang N, Klasing KC: Rice expressing lactoferrin and lysozyme has antibiotic-like properties when fed to chicks. J Nutr. 2002, 132: 1214-1218.PubMedGoogle Scholar
- Osserman EF, Lawlor DP: Serum and urinary lysozyme (muramidase) in monocytic and monomyelocytic leukemia. J Exp Med. 1966, 124: 921-952. 10.1084/jem.124.5.921.PubMed CentralView ArticlePubMedGoogle Scholar
- Schagger H, Aquila H, Von Jagow G: Coomassie blue-sodium dodecyl sulfate-polyacrylamide gel electrophoresis for direct visualization of polypeptides during electrophoresis. Anal Biochem. 1988, 173: 201-205.View ArticlePubMedGoogle Scholar
- Andra J, Berninghausen O, Wulfken J, Leippe M: Shortened amoebapore analogs with enhanced antibacterial and cytolytic activity. FEBS Lett. 1996, 385: 96-100. 10.1016/0014-5793(96)00359-6.View ArticlePubMedGoogle Scholar
- Quintela JC, Pittenauer E, Allmaier G, Aran V, de Pedro MA: Structure of peptidoglycan from Thermus thermophilus HB8. J Bacteriol. 1995, 177: 4947-4962.PubMed CentralPubMedGoogle Scholar
- Glauner B: Separation and quantification of muropeptides with high-performance liquid chromatography. Anal Biochem. 1988, 172: 451-464.View ArticlePubMedGoogle Scholar
- Hauser H, Howell K, Dawson RM, Bowyer DE: Rabbit small intestinal brush border membrane preparation and lipid composition. Biochim Biophys Acta. 1980, 602: 567-577. 10.1016/0005-2736(80)90335-1.View ArticlePubMedGoogle Scholar
- Leippe M, Ebel S, Schoenberger OL, Horstmann RD, Muller-Eberhard HJ: Pore-forming peptide of pathogenic Entamoeba histolytica. Proc Natl Acad Sci U S A. 1991, 88: 7659-7663.PubMed CentralView ArticlePubMedGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original URL.